Method of sintering briquetted materials



Aug. 15, 1933. c. R. SHORT METHOD OF s msnme BRIQUETTED MATERIALS FiledFeb. 24, 1930 Clrarles Ska-i.

' Patented Au 15,1933

umrao STATES PATENT, OFFICE METHOD OF SINTERING BBIQUETTED MATERIALSCharles a. Short, Dayton, Ohio, assignor to Moraine Products Company,Dayton, Ohio, a

Corporation of Ohio Application February 24, 1930. Serial No. 430,834

6 Claims.

This invention relates to the art of heat-treating or sintering metalstructures such as briquetted metal powders. q As disclosed in Patent1,642,348 to Williams et al, issued Sept. 13, 1927, finelydivided'metals such as copper, tin and zinc and a volatile fluxingmaterial have heretofore been mixed together in various combinations andproportions according to the desired characteristics of the product- Themixture may also include finely divided graphite and volatilevoid-forming substances, especially when greater porosity is de-' periodto sinter the metals together and are then removed and cooled down.Oxidation of the metal constituents of the briquettes is prevented bythe enveloping charcoal bed. Instead of sintering in packed charcoalboxes, the briquettes may be immersed in a fluxing liquid which is alsothe heating medium, for example, molten potassium cyanide. Of course,when so immersed, all oxidation of the briquettes is prevented.

The present invention has for an object to provide a novel method ofsintering such briquettes which is very much more rapid and economicalthan prior methods and which produces sintered bodies having greaterstrength and greater uniformity in physical properties.

Further objects and advantages of thepresent invention will be apparentfrom the following description, reference being had to the accompanyingdrawing wherein a preferred embodiment of one form of the presentinvention is clearly shown. V

In the drawing:

Fig. l is a longitudinal vertical section through a continuous sinteringfurnace for carrying out the methods of this invention.

Fig. 2 is a transverse section on line 2-2 of Fig. l.

Fig. 3 is a detail view taken on line 3-3 of Fig. 2 and illustrates thedirect contact of the pyrometer element with the briquette containerwhen said container is being rapidly heated in the quick-heating chamberof the furnace.

Similar reference characters refer to similar parts throughout thevarious views.

The furnace comprises a quick-heating chamber 10 and a main sinteringchamber 11, both of which are enclosed by suitable heat retaining wells12.

A continuous track 15 extends entirely through both chambers 10 and 11and projects out at 16 at the entrance opening 20 of the furnace and at17 at the exit opening 21 thereof. The wall 22 dividing chambers 10 and11 is provided with anopening 25 which is suffi-o 'ciently large for thebriquette containers 26 to easily pass therethrough along the track 15.Both chambers 10 and 11 have a false bottom wall 13 therein, under whichare the regulated gas burners or outlets 18 and 19. The burners 18supply heat to the quick heating chambers 10- and are separatelyregulated from the burners-19 which supply heat to the sintering chamber11. By this means the entrance chamber; 10, is maintained at asubstantially higher temperature than the sintering chamber 11, wherebyeach container 26 of briquettes 30 on entering the furnace is quicklyheated to the desired temperature before it is passed on into thesintering chamber which is maintained at the desired sinteringtemperature.

In the operation of the furnace, a large num ber of closed containers 26is provided. These containers are loaded with an-equal weight of thebriquettes 30. The filled containers 26 are then set upon the projectingtrack 16 and pushed one at a time into the quick-heating chamber 10,

' perature, the second receives a preliminary heating in position A. Animportant feature of the invention is the direct measuring of thetemperature of the container 26 during its quick heating 9 so that eachcontainer is heated quickly to an accurately controlled predeterminedtemperature before it is passed on into the sintering chamber 11. Fordirectly measuring the temperature of the container 26 while it is beingrapidly heated to, or approximately to the desired sintering tem-.perature, a pyrometer element '35 is pivotally mounted at 36 andweighted by a weight 37 so that its thermo-couple 38 will be urgedupwardly and contact directly upon the bottom of each container 26 whenit is in position 3" (see Fig.1) The electric wires 39 of the pyrometerlead to a visible temperature indicating, and also preferably recording,device in easyview of the operator.

When the operator notes that the container 26 mined temperature heimmediately pushes it along track l5.through theopening 25 into themain'sintering, chamber 11. Ordinarily this is done by placing a newlyfilled container 26 on' the projecting track'portion 16 and by means ofa a suitable rod pushing the entire line of containers a distance of oneposition. This of course will eject the last 'container 26 through theexit opening 21 of chamber 11, and move the con-.

in position B has reached the desired predete'rtainer in chamber 10 fromposition A to position B.

As one example of the material of the briquettes 30 the following isgiven:

Parts Copper powder 90 Tin powder 10 Salicylic acid 6 Ammonium chloride0.53

indicated by the pyrometer, it is pushed into the sintering chamber 11.It is preferred to heat the briquettes in chamber 10 from roomtemperature to sintering temperature as rapidly as possible consistentwith substantially'uniform heating of all the briquettes in a containersince it is found that the strength of the sintered bearing is greatlyincreased by such rapid heating. -If now it requires six minutes to heatthe containers from room temperature to 1450 F., a container will bepushed from chamber 10 into chamber 11 every three minutes. Now sincethere are six positions in chamber 11, each container will remaintherein for 18 minutes, during which timesintering of the powderedmaterials of the briquettes takes place. The ammonium chloride thereinvolatilizes during sintering and fills the containers 26 with a gaseousflux which also of course ejects the air from said containers at thecrevices around the covers and so provides a non-oxidizing atmospheretherein. I 1

The actual time required in thechambers of the-furnace will varychieflyaccording to the weight and shape of the briquettes; forinstance, if the briquettes have a thick heavy portion they obviouslycannot be heated so rapidly in chamber 10. A very important feature ofthe method of this invention is the substantially exact temperaturecontrol of ,the material in the container 26 in position B in chamber 10whereby the highly desirable uniformity of the sintered bushings isobtained. Heretofore standard practice in heat- 1 treating furnaces isto maintain the furnace chamber at a given temperature and to move thearticles being heat-treated therethrough on a time cycle. Obviously thismethod will not fix or control the exact temperature ofthe article beingtreated, especially if there -is any variation in the size or thicknessof the articles. The method of this invention does not rely on a timecycle at all, but proceeds "by measuring directly the fundamental factorin the heat treatment of the material, that is the temperature of the.article itself.

While the form of embodiment of the present invention as hereindisclosed constitutes ,a preferred form. it is to be understood thatother forms may be adopted, all coming Within th scope of the claimswhich follow.

. from finely divided metals, comprising: rapidly heating the articlesto a temperature near a predetermined sintering temperature by exposingthem to a temperature higher than said sintering temperature, and thensubstantially immediately passing said heated articles into a sinteringzone where they are maintained at the sintering temperature-untilsintered.

2. The method of sintering articles briquetted from finelydividedmetals, comprising: heating the articles substantially as rapidlyas possible consistent with the uniform heating of said articles to atemperature near a predetermined sine tering temperature by exposingsaid articles to a temperature higher than said sintering temperature,and then quickly passing said heated articles into a sintering zonemaintained at the sintering temperature and permitting said articles toremain in said sintering zone until sintering is completed.

3. The method of sintering highly compressed briquettes of finelydivided metals such as copper, tin and zinc, comprising: heating thebriquettes to a predetermined temperature near the desired sinteringtemperature at a high rate of tempera-.

ture change by exposing the briquettes to a temperature higher than thesintering temperature.

reached thereafter substantially immediately exposing said briquettes tothe sintering temperature for a period of time until the metal powdersare sintered together.

4. The method of sintering articles of briquetted metal powders,comprising: exposing a plurality of articles in a thin wall metalcontainer to a temperature considerably hotter than the desiredpredetermined sintering temperature, directly measuring the temperatureof said container as it rapidly rises due to such heating and when saidcontainer approaches said sintering temperature, passing it quickly intoa sintering zone maintained at the desired sintering temperature wheresintering occurs for a period of time.

5. The method of sintering articles briquetted from finely dividedmetals comprising: inserting a plurality of said articles in a thin wallmetal container and then heating said container and- 'ing of saidarticles by exposing them to a temperature higher -than a predeterminedsintering temperature until the temperature of the articlesapproachesmaidsintering temperature, and then quickly passing saidheated container and articles therein into a sintering zonemaintained atsaid sintering temperature and permitting said articles to remaintherein until sintering is completed.

6. The method of sintering articles briquetted from finely dividedmetals, comprising} first,

rapidly heating the articles to a temperature near a predeterminedsintering temperature in a quickheating zone having such a high rate ofheat supply thereto that said articles would be quickly heated beyondsaid sintering temperature if they remained therein after reaching saidsintering temperature, then substantially immediately passing saidheated-articles into a sintering zone,

maintained at-said predetermined sintering temperature 'and permittingsaid articles to remain thereinuntil sintering is completed.

